kdlewis1975 wrote:
...just to add to warp2diesel's chemistry lesson....
About 10 years ago early in my college career, I was a co-op employee at a refinery pilot plant for the former Ashland Petroleum. The project at the time making research variety of base lubes for Valvoline to experiment with for blending into motor oils. The final step before wax removal was hydrotreating. I recall that the sulfur level had to be under something like 5 ppm if I'm remembering correctly. Among the numerous reasons for wanting sulfur low, one I was given that it affected the viscosity profile and its consistency.
Their pilot plant set-up was a continuous reactor. The feed went into a column packed with catalyst and was heated to 450 deg F. Hydrogen was fed in at 1000 psi. I don't know what they specifically did for gasoline and diesel, but I'll hazard a guess that it's just some variant of this. I imagine all the refiners did to meet the sulfur mandate was to alter temperatures, pressures, feed rates, and maybe the catalyst too.
While hydrotreating is aimed at sulfur removal, the process also removes unsaturation (can help shelf life) and takes out a small portion of the aromatic compounds.
On the occasion of actually going down to the refinery, I remember there being mounds of elemental sulfur piled everywhere. I think they pretty much have to "give it away" since there isn't a huge market for it outside of tires or conversion into sulfuric acid.
It is amazing how many elements and compounds are totally essential for Human, Animal, and Plant Life, but are considered pollutants. Pull the Sulfur out of Diesel, Gasoline, Coal Exhaust so we can spread it on our crop land so the plants grow right and the livestock that eat them don't get sick and die. I can see some of the motivation behind the pharmaceutical industry to keep us a little sick so they can sell their solutions even when the solutions nature provides are cheaper. For me, I eat 2 oz of Almonds or Walnuts or Pistachios or Pecans every day instead of taking Zocor. They taste better too.
I must hand it to Bosch for being honest about why we need the low sulfur fuel, it attacks the catalyst, not because of some health issue. I am sure CARB would argue that point.